(define (check-num x)
  (cond ((< x 0) "Negative")
        ((= x 0) "Zero")
        ((> x 0) "Positive")))

(display (check-num -5))  (newline)  ;; "Negative"
(display (check-num 0))  (newline)  ;; "Zero"
(display (check-num 10)) (newline)  ;; "Positive"


(define (grade-score score)
  (cond ((>= score 90) "A")
        ((>= score 80) "B")
        ((>= score 70) "C")
        ((>= score 60) "D")
        (else "F")))

(display (grade-score 85)) (newline)  ;; "B"
(display (grade-score 55)) (newline)  ;; "F"
